This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application THIN-FILM BAND PASS FILTER AND METHOD FOR MANUFACTURING IT filed with the Korean Industrial Property Office on Oct. 15, 1999 and there duly assigned Ser. No. 1999/44752
1. Field of the Invention
The present invention relates to a bandpass filter that filters an input electrical signal to pass only signals in a specific frequency band, and more particularly to, a thin-film bandpass filter in which a spiral inductor and a capacitor are formed in a thin-film shape, and a manufacturing method thereof.
2. Description of the Related Art
In general, bandpass filters use a principle that impedance in combination of an inductor and a capacitor changes depending on a frequency. In other words, since a resonant frequency f0 equals   1      2    ⁢          xe2x80x83        ⁢    π    ⁢                  L        ⁢                  xe2x80x83                ⁢        C            
when an inductor L and a capacitor C are connected in series, a filter for passing only signals of a specific frequency band may be embodied by repeating the arrangement of the inductor L and the capacitor C. As a filter operated within the range of a microwave frequency of 500 MHz or higher, a thin-film microwave bandpass filter, as shown in FIG. 1, has been proposed. The thin-film bandpass filter consists of a plurality of capacitors 32 formed by appropriately stacking and arranging a metal layer and an insulating layer on a planar substrate 12, a plurality of spiral inductors 10, and electrical connection. In this case, the spiral inductors 10 and capacitors 32 are electrically connected in series, alternately, by a lead pattern, and the spiral inductors 10 are disposed at the ends. As shown in FIG. 2, each capacitor 32 includes a pair of first metal layers 34 and 36 which are separated by a predetermined gap G on the planar substrate 12, an insulating layer 40 formed on at least a portion of the top surface of the first metal layers 34 and 36, a second metal layer 42 overlapping the first metal layers 34 and 36 and formed on the top surface of the insulating layer 40.
As shown in FIGS. 1 and 3, each spiral inductor 10 is formed in a spiral shape and including first and second traces 22 and 24 comprised of first metal layers 16 and 18 formed on the planar substrate 12, a connection bridge 28 comprised of a second metal layer 18, overlying the first metal layers 16 and 18 and connecting between the first and second traces 22 and 24, and an insulating layer 20 for insulating the intersection portion.
The first trace 22 is looped into a coil and ends at an interior end 26. The second trace 24 is disposed parallel and adjacent to the periphery of the first trace 22. The connection bridge 28 contacts the interior end 26 of the first trace 22 while being connected to the second trace 24 across an intermediate portion 30 of the first trace 22. In this case, the insulating layer 20 isolates the connection bridge 28 from the intermediate portion 30 of the coiled trace. Reference numerals 1 and denote contact pads. The thin-film bandpass filter described above has a structure in which the spiral inductors 10 and the capacitors 32 are alternately connected in series between the contact pads 1 and 5.
Since the conventional thin-film bandpass filter has a two-dimensional structure in which the inductors are attached to the substrate 12, a parasitic capacitance is generated between the inductors 10 and the substrate 12 to a great extent, and accordingly, the Q factor of the inductor 10 is reduced. Therefore, the conventional bandpass filter has smaller resonant frequency of the inductor 10 itself. Accordingly, the inductor 10 is of a narrower range for use. Also, the insertion loss of the bandpass filter is increased. Thus, the conventional thin-film bandpass filter has a drawback in that a process of amplifying a signal that passes through the filter is further required. Furthermore, there is another problem in that the overall size of the bandpass filter is large since inductors and capacitors are connected in series with the plane substrate 12 unfolded. However, when such a bandpass filter is implemented on a semiconductor chip, the filter consumes a large amount of precious space. In addition, the inductor may contain a parasitic capacitance which is unwanted. Furthermore, the insertion loss of the filter may be high, there may be a low resonant frequency, and the cost for manufacturing the bandpass filter may be excessive.
What is needed is a design for a bandpass filter implemented on a semiconductor chip, that is small, has a low manufacturing cost, low insertion loss, a higher resonant frequency, and eliminates the problem of parasitic capacitances.
It is therefore an object of the present invention to provide an improved design and an improved method of manufacture of a thin film bandpass filter.
It is also an object of the present invention to provide a bandpass filter that is space efficient. It is yet another object of the present invention to provide a bandpass filter that is easy and inexpensive to manufacture.
It is still an object of the present invention to provide a thin film bandpass filter that has a low insertion loss.
It is still yet another object of the present invention to provide a thin film bandpass filter that reduces and eliminates parasitic capacitances.
It is yet also an object of the present invention to provide a semiconductor bandpass filter that has a higher resonant frequency.
Accordingly, to achieve the above object, the present invention provides a thin-film bandpass filter including: a substrate; a plurality of first capacitors formed on the substrate, each being electrically connected in series; at least one second capacitor electrically connected to branch terminals positioned between the plurality of first capacitors; an inductor electrically connected in parallel to the second capacitor; and a plurality of supports for propping up the inductor so that the inductor is separated a predetermined space above the substrate and/or the second capacitor. The first and second capacitors, respectively, include a first metal layer, a dielectric layer, and a second metal layer, all of which are sequentially formed on the substrate. The inductor is comprised of a predetermined pattern of a thin-film metal layer propped by the plurality of supports, to both ends of which are electrically connected to the first and second metal layers of the second capacitor, and suspended by the substrate and/or the second capacitor.
Furthermore, the inductor includes a spiral inductor portion having at least one turn, formed in a flat spiral shape above the supports and propped by the supports; a first connecting portion for electrically connecting an interior end of the spiral inductor portion and one metal layer of the second capacitor, the first connection portion including a vertical portion extending downward from the interior end of the spiral inductor portion, and a horizontal portion extending from one side of the vertical portion to be separated from the spiral inductor portion; and a second connecting portion for electrically connecting an exterior end of the spiral inductor portion and the other metal layer of the second capacitor, the second connection portion including a vertical portion extending downward from the exterior end of the spiral inductor portion. In this case, preferably, at least a portion of the supports are formed on the second capacitor and at least a portion of the spiral inductor portion of the inductor is positioned above the second capacitor.
The present invention also provides a method of manufacturing a thin-film bandpass filter including the steps of: preparing a substrate; sequentially providing a first metal layer, a dielectric layer and a second metal layer at predetermined positions on the substrate to form a plurality of first capacitors, each of which is independent, and at least one second capacitor; providing a plurality of contact pads and a lead pattern on the substrate to form an electrical connection structure between the first and second capacitors so that the first capacitors are electrically connected in series to each other by the lead pattern and the second capacitor is connected to a branch terminal formed between the first capacitors; forming a plurality of supports having a predeterminedheight on the substrate and/or the second capacitor; and forming an inductor including first and second connecting portions electrically connected to the first and second metal layers of the second capacitor, and an inductor portion formed of a predetermined pattern of a metal layer on the supports and propped by the supports, and in which both ends of the inductor portion are connected in parallel to the second capacitor by the first and second connecting portions. In this case, preferably, at least a portion of the supports are formed on the second capacitor and at least a portion of the inductor portion is positioned above the second capacitor. The method further includes the step of forming an insulating layer on a region of the second capacitor excluding a portion for electrically connecting the inductor portion and the first and second metal layers.
The first connecting portion comprises a first vertical portion extending downward from an interior end of the inductor portion, and a horizontal portion extending from one side of the second vertical portion, separated from the inductor portion, and electrically connected to one metal layer of the second capacitor. The second connecting portion comprises a second vertical portion extending downward from an exterior end of the inductor portion and electrically connected to the other metal layer of the second capacitor. The step of forming the inductor includes the steps of: forming a position pattern of the second vertical portion of the second connecting portion and the horizontal portion of the second connecting portion using a photoresist to provide a lower metal layer at the positions of the second vertical portion and the horizontal portion; forming a position pattern of the first vertical portion of the first connecting portion and the second vertical portion of the second connecting portion using a photoresist to provide an upper metal layer at the positions of the first and second vertical portions; providing a metal layer in a predetermined pattern on the photoresist layers and the upper metal layer to form the inductor portion; and removing the photoresist layers. In this case, the supports are comprised of the same metal material as the vertical portions of the first and second connecting portions, and a support position pattern is formed and then the lower and upper metal layers are formed at the support position, in the step of forming the vertical portions of the first and second connecting portions.